1. Field of the Invention
The present invention relates to a toner to be used for developing an electrostatic latent image to be formed in an image forming method such as an electrophotographic method, an electrostatic recording method, a magnetic recording method, or a toner jet recording method.
2. Description of the Related Art
A large number of methods have been conventionally known as electrophotographic methods. A general electrophotographic method involves the steps of: using a photoconductive substance to form an electrostatic latent image on an electrostatic charge image-bearing member (which may hereinafter be referred to as the “photosensitive member”) through various means; developing the latent image with toner to form a toner image which is transferred as required onto a recording medium such as paper; and fixing the toner image onto the recording medium by means of heat, pressure, or the like to produce a copied article.
In recent years, analog printers and copying machines have been replaced with digital printers and copying machines. Accordingly, excellent reproducibility of a latent image, high resolution, an increase in printing speed, and a reduction in power consumption have been strongly demanded. For example, when attention is paid to a printer, a ratio of power consumption in a fixing step to the total power consumption is considerably large, and an increase in fixing temperature inevitably increases power consumption. Furthermore, a high fixing temperature involves a problem such as the curling of paper which is to be printed out, so a reduction in fixing temperature has been strongly desired.
A large number of studies have been conventionally made on the fixation of toner at a low temperature. For example, the incorporation of wax as a releasing agent into toner is well known. However, toner containing such releasing agent is apt to deteriorate owing to high degree of duration, although the toner has an expanded temperature region in which fixation can be performed. In addition, the durability of the toner may be insufficient for long-term stable use.
In view of the above, JP 05-273794 A proposes a toner in which filming is suppressed and which provides an image capable of maintaining a high density and high quality for a long time period. In the toner, the value of a ratio Os/Cs in surface composition determined by toner surface analysis and the average lattice length of the toner measured by means of small-angle X-ray scattering are specified.
JP 11-282196 A proposes a toner in which the layer thickness of a lamellar structure to be formed in a wax domain in toner particles is specified in a particular range to improve the low-temperature fixability, offset resistance, and durability of the toner. However, only an approach based on a releasing agent hardly provides toner performance that can sufficiently cope with recent trends, in other words, an increase in speed of a printer and energy savings.
Meanwhile, some toners that are allowed to be capable of being fixed at low temperatures by an approach except the approach based on a releasing agent have been proposed. For example, JP 04-184358 A proposes a small-particle-size toner containing crystalline polyester, the toner being capable of forming an image excellent in fixability and having high resolution. JP2002-287426 A proposes a technique involving adjusting the dispersion domain diameter of crystalline polyester in toner containing the crystalline polyester and an amorphous resin, to provide an image having excellent low-temperature fixability, good storage stability, and high quality. JP 2002-49180 A proposes a toner obtained by salting-out/fusing composite resin particles and colorant particles, in which crystalline polyester is incorporated into a region except the outermost layer of a composite resin particle. The toner provides: a wide fixing temperature region; and excellent durability to prevent filming, fogging, carrier spent, or the like from occurring. There has been also proposed a technique involving adjusting an abundance ratio between the amount of a releasing agent and the amount of a low-softening-point substance in each of the vicinity and inside of the surface of toner containing the releasing agent and the low-softening-point substance, to achieve compatibility between fixability and offset property.
However, none of those conventional toners has sufficiently achieved compatibility between durability in long-term use and low-temperature fixability, and each of them is still susceptible to improvement in terms of storage stability. In particular, when an image forming process speed is high, the time during which toner and a fixing unit are in contact with each other upon fixation is extremely short, so the amount of heat that the toner receives is limited. Therefore, toner to be used for a high-speed printer is requested to have improved low-temperature fixability.